In recent years, highly integrated semiconductor devices, smaller mounted areas, and lowering interconnection resistances by reducing interconnection distances have been in high demand due to high-performance and compact electron equipment, such as cell-phones and IC cards. To obtain these, stack structures in which semiconductor elements are stacked in a vertical direction have been developed.
One example of methods for producing stack structures is a method including steps of: thinning a wafer on which a semiconductor element is formed; providing a through-hole with a technique such as anisotropic dry etching (through silicon via: TSV technique); forming an electrode on the rear surface of the wafer by filling the through-hole with a conductive material such as copper; forming a passivation film on the rear surface having an electrode; and electrically joining the wafer and a chip or the surface of a wafer on which another semiconductor element is formed.
In the steps above, the insulating film formed on the rear surface of a wafer is required to be electrically insulative to prevent current leakage and migration of a conductive material, to be solvent-tolerant and have a good dry etch back property in a photolithography step that is to open an electrode portion after forming a passivation film, and to be heat-tolerant in an electrode-joining step.
Examples of well-known passivation films include benzocyclobutene resins, polyimides, and fully aromatic polyethers.
However, benzocyclobutene resins require a fluorine gas to be used for dry etch back in a photolithography step, and thus electrodes and wafers may be damaged. In addition, cross-linking reaction does not sufficiently proceed at a curing temperature around 200° C., and a good solvent-tolerance cannot be obtained.
In contrast, as for polyimides, thinned wafers may be damaged because the film-forming temperature is 300° C. or higher, and shrinkage of films upon curing results in remaining stresses.
Fully aromatic polyethers have no heat cross-linking portion, and thus are not highly tolerant of solvents. In addition, resins may be melted in joining electrodes because the resins have low softening points.
A substrate for a thick film technique has been disclosed (Patent Document 1). In the substrate, an undercoat film containing 30% by volume to 45% by volume of a polyether ether ketone resin powder and a thermosetting resin is formed on an inorganic insulating substrate that is a glass base material impregnated with a silicone resin.
Covering products, such as an adhesive for flexible printed-circuit boards, that contain a polymer having a main chain composed of a polyimide, and having a functional group having a carbon-carbon triple bond at an end thereof, have been disclosed (Patent Document 2).
Covering products, such as an adhesive composition containing a polymer having a main chain containing a functional group having a phenyl group, urea, an amido group and the like, and a carbon-carbon triple bond, have been disclosed (Patent Document 3). Covering products, such as an adhesive composition containing a polymer containing polyether ether sulfone having a sulfonic acid group, and containing polyether ether ketone, have been disclosed (Patent Document 4).